Optical fiber connectors are an essential part of practically all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices such as radiation sources, detectors and repeaters, and to connect fiber to passive devices such as switches and attenuators. The principal function of an optical fiber connector is to optically couple a fiber with an optical pathway of a mating device (e.g., another fiber, an active device or a passive device) by holding the end of the fiber, typically in a ferrule, such that the core of the fiber is axially aligned with the optical pathway of the mating device.
Optical connectors may be classified as either pull-proof or non-pull proof. In a pull-proof connector, the cable's jacket (and its strength members, if any) is secured to the housing of the connector. Accordingly, if a tensile load is applied to the cable, the load will be transferred from the cable's jacket to the housing. The load is therefore not transferred to the ferrule assembly within the housing. Accordingly, after the connector is mated, the ferrule assembly will not be affected (i.e., drawn back) by a tensile load applied to the cable, and thus the fiber in the ferrule will continue to make contact with the optical pathway of the mating device. On the other hand, in a non-pull proof connector, the cable jacket is secured to the rear portion of the ferrule assembly. Accordingly, when a tensile load is applied to the cable, the load on the jacket is transferred to the rear portion and thus directly to the ferrule assembly, which slides or “floats” within the housing.
Although pull-proof connectors are generally preferred because of their resilience to tensile loads applied to the cable, non-proof connectors are preferred when using tight-jacketed cable. Tight-jacketed optical fiber cable (herein tight-jacketed cable) is well known and comprises an optical fiber adhered to a surrounding, tough polymer jacket. Unlike typical buffered cable, the fiber in a tight-jacketed cable is not free to move within its protective covering. Because a tight-jacketed cable does not allow the optical fiber to move independently of the jacket, it has been recognized that the jacket and the fiber should be anchored to a common component in the connector such that there is no relevant movement between the fiber and the jacket. Accordingly, both the fiber and the jacket are anchored to the ferrule assembly in non-pull proof connectors. (See, e.g., US Patent Application Publication No. 20070292084 for details.)
Another component of a conventional optical connector is a boot for limiting bending of the fiber. By way of background, in routing either cables or single fibers, it is imperative for reliable signal transmission that sharp bends in the fibers be avoided. A sharp bend (i.e., small radius) in a fiber can lead to signal loss by virtue of at least some of the transmitted light leaking out of the fiber at the bend. A sharp bend can also cause further signal degradation if the bend introduces microcracks in the fiber, which reduce or impair the uninterrupted guiding of the optical signals. An excessively sharp bend may even cause fiber breakage.
To prevent excessive bending, bend-limiting boots, or simply boots, are used. For example, referring to FIG. 3, a prior art LC type, non-pull proof connector 300 is shown comprising a boot 304, which is elongated and exteriorly tapered, and has bend-limiting segments separated from each other by gaps 315. The boot extends from the rear portion 301a of the ferrule assembly 301 and defines an internal channel 313 through which the cable passes. The boot slips over the rear portion 301a of the ferrule assembly 301 of the connector, and protects the cable from excessive bending at the region where it enters the connector. Specifically, when the cable is bent, the segment portions on the inside of the bend are forced toward each other until they touch, thereby preventing further bending. Properly designed, the boot prevents the cable from approaching the critical bend radius for the fiber or fibers therein.
Although connector 300 has performed well over the years, recently, Applicants have recognized a trend that connectors used with active components and in backplane applications have a disproportionately high failure rate, especially when used in high-density applications. These failures are caused, in general, by damaged optical components within the mating devices. Noteworthy is the fact that this high failure rate is associated with mating devices having “fixed” optical interfaces, such as fixed ferrules used in transceivers and backplane connectors.
Applicants surmised that these failures occur more frequently in high-density connector applications because installers use the boot to push the connector forward to effect mating. That is, in such high density applications, there is insufficient room around the connector for an installer to grasp the housing and push it forward such that the connector engages and mates with the mating device. Instead, the installer typically uses the boot, which extends rearwardly from the connector, to force the connector forward. Because the boot is typically secured to the ferrule assembly in a conventional non-pull proof connector, the forward force applied to boot is transferred to the ferrule assembly. This force can be many times higher than the normal biasing force applied to the ferrule assembly by virtue of the spring, which is engineered to provide the proper mating force. Accordingly, pushing the connector forward into a mating device having a fixed optical interface may result in much higher than expected mating force because the optical components of the fixed optical interface cannot “backup” in response to higher than expected mating forces. The pressure between the ferrule assembly and these optical components can increase significantly, possibly resulting in damage to either the connector, the mating structure, or both.
In addition to causing damage to the optical components, Applicants also recognize that using the boot to push a non-pull proof connector forward to mate tends to be ineffective. Specifically, referring back to FIG. 3, when pushing the boot forward to mate the connector, the ferrule 303 of the connector stops against the fixed optical interface of the mating device before the housing 302 engages and mates with the mating device (not shown). Because the boot 304 is attached to the ferrule assembly 301 and not the housing 302, once the ferrule abuts the fixed optical interface, pushing the boot does nothing to advance the housing forward. Additionally, because the ferrule assembly 301 is biased forward in the housing 302, this biasing actually urges the housing backward away from the mating device, thereby making contact between the housing 302 and the mating device even more difficult.
A need therefore exists for a non-pull proof connector having a boot that is configured to allow the user to mate the connector by pushing the boot forward. The present invention fulfills this need among others.